Great progress has been made over the past decade in elucidating pathophysiologic mechanisms in airways inflammatory diseases. Considerable controversy remains however, relating to the specific role of chemokines and their receptors in orchestrating the pathology. During the last funding cycle of this grant, we focused on two beta chemokine receptors, CCR1 and CCR3, examining their role, through the use of mice with genetic deletions, in several well-characterized models of lung disease. We additionally characterized eosinophil lineage ablated mice (?dblGATA) in both acute and chronic models of allergic airway inflammation. Our data support CCR3 ligation as the dominant mechanism for eosinophil recruitment, at baseline as well as in response to injury or infection. Using the ?dblGATA mice, we demonstrated that allergic airway hyperresponsiveness occurs in the absence of eosinophils, but that these cells may control features of airway remodeling. In Specific Aim 1 of this renewal application, we propose experiments to determine whether CCR3-/- mice are similarly protected from allergic airway remodeling. In preliminary studies we find a potential role for CCR1 in the pathophysiology of RSV infection, although complexities are revealed by superimposition of an allergic reaction. In our focus on airway hyperresponsiveness and the role of eosinophils, the newly gleaned variability in the role of this cell type appears to derive from subtleties in the mode of administration and nature of the allergen, as well as background mouse genetics. Since mice (and humans) develop airway hyperresponsiveness to RSV in the absence of an adaptive immune reaction, we have opted to investigate this mechanism of airway injury. We hypothesize a significant role for the fractalkine/CX3CR1 axis in RSV lung disease and will define the mechanism by which the RSV G glycoprotein subverts innate immune responses. Successful completion of these studies will provide additional mechanistic understanding of the pathophysiology of RSV induced lung injury as well as preclinical validation for drug development. PUBLIC HEALTH RELEVANCE: Since mice (and humans) develop airway hyperresponsiveness to RSV in the absence of an adaptive immune reaction, we have opted to investigate this mechanism of airway injury. We hypothesize a significant role for the fractalkine/CX3CR1 axis in RSV lung disease and will define the mechanism by which the RSV G glycoprotein subverts innate immune responses. Successful completion of these studies will provide additional mechanistic understanding of the pathophysiology of RSV induced lung injury as well as preclinical validation for drug development.